The griffin is immortal.

Once again, regarding the demon castle in the second mission. There is a FLAG near the first castle; visit it, and it will unlock.
As for the choice, it's this: either you go to the church, which blocks the altar, or you go to the altar, which blocks the church. Accordingly, visiting the altar unlocks the vampires, and visiting the church unlocks the angels.

But how is the player supposed to know about the flag and the choice with the angels/vampires? I don't think I'm alone in saying that I didn't find out from the chat with the author. I happened to approach the angels earlier, but I didn't understand at all that a decision had been made. As a rule, maps use dialogue boxes with a description of the consequences of the decision (OK - one option, Cancel - another), for example, I recently encountered this in "Archdevil." I, for example, vaguely remember something about the altar in the text (vaguely, because it's not even briefly mentioned anywhere) and thought that a choice had to be made there, and maybe even Markel had to sacrifice a unit. As for the flag, it's just fantastic to guess. But it would be nice to have some kind of sensible system for structuring and describing tasks and the possibility of making a conscious choice if there are several plot options.